Amplifier



's. E. ADAIR.

AMPLIFIER.

I APPLICATION FILED AUG-14,1919. 1,388,275 Patented July 5, 1921.

T Fl 5.1-

WITNESSES UNITED STATES PATENT OFFICE.

SAMUEL n ADAIR, or NEW YORK, N. Y., ASSIGNOR TO mrnmmriouar. aamo mn- GRAPH comrm, A coaroaanon or DELAWARE.

AMPLIFIER.

T all w ham it may concern:

Be it known that I, SAMUEL E. ADAIR,

, a resident of New York, in the county of "New York and State of New York, have invented a new and useful Improvement in Amplifiers, of which the following'is a specificat-ion.

The invention relates to an amphfier for electrical currents of all kinds, either varying or continuous.

. he object of the invention is to provlde an amplifier, employing a tri-electrode device, which is capable of be ng worked 1n successive stages of amplification, and which is free from oscillation disturbances, which result in producing what is known as a howl, and also free from interference with the normal operation of the device due to the production of a negative charge on the gri l In the accompanying drawings Flgure 1 is a diagram showing a simple form of the amplifier connected to a radio signal receiving antenna for amplifylng the signal mpulses and which will explain the principle of the invention, and Fig. 2 is a similar diagram showing a number of the amplifiers connected in series to produce successive stages of amplification.

The invention utilizes "amplifiers of the tri-electrode type such as the well known vacuum tubes containing three electrodes, to

- 'wit, a plate electrode, a heated electrode or filament, and an interposed grid electrode. Usually these electrodes are contained in a.

vacuum tube,'such as in the well known audion, but more recently tri-electrode devices of this kind capable of being operated in open air have been produced. Th1s invention can utilize either tri-electrode devices.

- ers; or by the resistance method. In the two last named types grid condensers are employed to prevent the positive potentlal of the plate battery from affecting the grid.

All of the above described methods are Specification of Letters Patent.

of said forms of' evices and which are worked in suc-' more, when grid condensers are used, strong signals produce an excessive negative charge on the grid, which seriously interferes with the normal operation of the tri-electrode device, commonly spoken of as paralyzing Patented July 5, 1921. Application filed August 14, 1919. Serial No. 317,394.

the tube. Efforts have been made to overcome this paralyzing effect by placing resistance leaks between the grid and the filament, but this seriously afi'ects the sensitiveness of the. amplification in the case of weak signals. Another undesirable characteristic which is always present in all of the above mentioned types of vacuum tube amplifiers is that they have a natural perlod as a whole, which requires that a particular adjustment be made for any particular frequency of alternating current in order to secure the most satisfactory results. This results. in additional complication and requires greater skill in order to secure satisfactory operation of the amplifiers. Another objection is that all the aforementioned types of amplifiers depend on a changing or varying current or in other words the coupling is ineffective unless the current to be amplified is varying or changing.

The principal object of the .presentinven;

tion is to overcome the above objections in the use of vacuum tubes or other tri-electrode devices of the same character. Gen erally stated the invention consists in connecting such tri-electrode device in one branch of a \Vheatstone bridge. A sim le diagram illustrating thisis shown in ig. 1, in which is diagrammatically shown a typical form of Wheatstone bridge and a typical form of a vacuum tube of the trielectrode tyipe. As here shown the reference X and Y illustrate the usual of, said filament being provided with the usual heating battery H. The circuit 0, carrying the impulses or electric I currents to be. amplified, is connected to the grid G, which, as'usual in devices of this kind, is interposed between the plate and the filament. This circuit 0 has its opposite side connected to the juncture of the branches A and X of the \Vheatstone bridge, and is shown as provided with a tuning condenser Gand has inserted in-it the secondary S of an oscillation transformer, the primary Q of which is shown as connected in a typical radio receiving circuit comprising the an tenna T connected to the ground at U, and including the variable tuning inductance V. This particular connection is intended to illustrate merely one use of the amplifier.

As is well known in the art when there is no potential upon the grid G, such' as when no signal impulses are being received, the circuit from the plate to the filament has a definite and constant resistance so that if the other elements ofthe lVheatstone bridge, consisting of the eleinents A, 15, X and Y, are balanced against this resistance through the tri-electrode device, a condition exists in which there. is no difference in potential between the points at which the galvanometer I (or other indicator) is ordinarily connected, that is, at the juncture of the resistance branches Y and B, and A and X respectively. If now a. potential is applied between the grid G and the filament F of the tri-electrode device, such as by the arrival of incoming signal impulses, the resistance of the path of conduction from the plate to the filament within the tube will be'changed, and this results in a proportional difference in potential across the galva-nometer or other indicator I, which difference in potential will be maintained aslong as the potential is applied to the grid G. To secure the best arrangement the relative values of the several resistances will, of course, be selected with regard to the resistance of the trielectrode device employed, as is well known I in the art. I

To secure a. further amplification by means of the device described, an arrangement will be employed in which several \Vheatstone bridges are connected in stages, one embodi-- ment being shownin Fig. 2. l lere'each-v individual amplifying unit is the same as that shown in Fig. 1, a common heating'battery being employed for the filament of all of the tri-electrode devices, with a variable re sistance R in each filament circuit to, control the degree of heating thereof. The galvanometer connection y of each bridge is carried the grid and filament of the next succeeding tri-electrode device, with the galvanometer connect-ions of the last bridge of the series connected respectively to the grid G and filament F of another tri-electrode device, and with a telephone T and local source E connected to the plate P and filament F of said final tri-electrode device.

By this arrangement the proportional difference in potential produced in the first bridge, by the effect of the incoming signal impulses on the grid of the first tri-electrode device, is carried over to the grid of the second tri-electrode device, thereby causing a proportional difference in potential across the second bridge which is greater than the difference of potential across the first bridge, due to the -energ'y added by the bridge-batteries in circuit. -Thisdifference ment to cause any internal howl characteristic of other tri-electrode amplifiers coupled in the manner heretofore employed.

The potential of the grid of any of the tri-electrode devices; except the first, can be.

made either negative or positive, by either raising or lowering the filament current of the preceding tri-electrode device by adjustment of the resistance device K. Thisresults: in ra-ising'or loweringthe direct current resistance of that particular tri-electrode device, thus unbalancing the bridge and causing a corresponding change inpotential across the grid and filament of the succeeding tri-electrode device.

Certain resistance elements employed by me in the bridge arrangements of amplifiers had approximately 48,000 ohms resistance each. These were of the type known to the trade as Lavite resistance units. They had a substantially negligible inductance, approximately 40 centimeters, and a capacity too small to be readily measured.

I claim:

1. Apparatus for amplifying electrical currents, comprising. a heatstone bridge having a tri-elect-rode device connected by its plate .and filament electrodesin one of the branches of said bridge, with the circuit carrying the current to be amplified connected between the grid and filament, and an indicator connected across said bridge.

2. Apparatus for amplifying electrical currents, comprising a Wheatstone bridge, a tri-electrode device connected by'its. plate and filament in one branch of said bridge and having its grid and filament connected to the circuit carrying the current to be amplified, another Wheatstone bridge having a tri-electrode device connected by its plate and filament in one branch thereof and having its grid and filament connected across the preceding bridge, and an indicatin device connected across the last bridge 0? the series.

3. Apparatus for amplifying electrical currents, comprising, in combination, a series of lVheatstone bridges each having a trielectrode device connected by its plate and filament in onebranch of the bridge, the grid and filament tof the first tri-electrode device being connected to the circuit carrying the current to be amplified, the grid and filament of each succeeding tri-electrode device connected across the preceding bridge, and a translating or indicating device connected to the late and filament of the last t'ri-electrode vice of the series. r

In testimony whereof, I have hereunto set y d- SAMUEL E. ADAIR.

Witnesses:

JOHN V. L. HOGAN, Gno. E. Conn. 

